Hydroxylated hierarchical flower-like COF for solid-phase extraction of adrenergic receptor agonists in milk

A new detection platform based on a hydroxylated covalent organic framework (COF) integrated with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was constructed and used for detecting adrenergic receptor agonists (ARAs) residues in milk. The hydroxylated COF was prepared by polymerization of tris(4-aminophenyl)amine and 1,3,5-tris(4-formyl-3-hydroxyphenyl)benzene and applied to solid-phase extraction (SPE) of ARAs. This hydroxylated COF was featured with hierarchical flower-like morphology, easy preparation, and copious active adsorption sites. The adsorption model fittings and molecular simulation were applied to explore the potential adsorption mechanism. This detection platform was suitable for detecting four α2- and five β2-ARAs residues in milk. The linear ranges of the ARAs were from 0.25 to 50 µg·kg-1; the intra-day and the inter-day repeatability were in the range 2.9-7.9% and 2.0-10.1%, respectively. This work demonstrates this hydroxylated COF has great potential as SPE cartridge packing, and provides a new way to determine ARAs residues in milk.

Molecular mechanism of inhibition of COVID-19 main protease by β-adrenoceptor agonists and adenosine deaminase inhibitors using in silico methods

Novel coronavirus (COVID-19) responsible for viral pneumonia which emerged in late 2019 has badly affected the world. No clinically proven drugs are available yet as the targeted therapeutic agents for the treatment of this disease. The viral main protease which helps in replication and transcription inside the host can be an effective drug target. In the present study, we aimed to discover the potential of β-adrenoceptor agonists and adenosine deaminase inhibitors which are used in asthma and cancer/inflammatory disorders, respectively, as repurposing drugs against protease inhibitor by ligand-based and structure-based virtual screening using COVID-19 protease-N3 complex. The AARRR pharmacophore model was used to screen a set of 22,621 molecules to obtain hits, which were subjected to high-throughput virtual screening. Extra precision docking identified four top-scored molecules such as +/--fenoterol, FR236913 and FR230513 with lower binding energy from both categories. Docking identified three major hydrogen bonds with Gly143, Glu166 and Gln189 residues. 100 ns MD simulation was performed for four top-scored molecules to analyze the stability, molecular mechanism and energy requirements. MM/PBSA energy calculation suggested that van der Waals and electrostatic energy components are the main reasons for the stability of complexes. Water-mediated hydrogen bonds between protein-ligand and flexibility of the ligand are found to be responsible for providing extra stability to the complexes. The insights gained from this combinatorial approach can be used to design more potent and bio-available protease inhibitors against novel coronavirus.Communicated by Ramaswamy H. Sarma.

Ligands of Adrenergic Receptors: A Structural Point of View

Adrenergic receptors are G protein-coupled receptors for epinephrine and norepinephrine. They are targets of many drugs for various conditions, including treatment of hypertension, hypotension, and asthma. Adrenergic receptors are intensively studied in structural biology, displayed for binding poses of different types of ligands. Here, we summarized molecular mechanisms of ligand recognition and receptor activation exhibited by structure. We also reviewed recent advances in structure-based ligand discovery against adrenergic receptors.

Mutual Enhancement of Opioid and Adrenergic Receptors by Combinations of Opioids and Adrenergic Ligands Is Reflected in Molecular Complementarity of Ligands: Drug Development Possibilities

Crosstalk between opioid and adrenergic receptors is well characterized and due to interactions between second messenger systems, formation of receptor heterodimers, and extracellular allosteric binding regions. Both classes of receptors bind both sets of ligands. We propose here that receptor crosstalk may be mirrored in ligand complementarity. We demonstrate that opioids bind to adrenergic compounds with micromolar affinities. Additionally, adrenergic compounds bind with micromolar affinities to extracellular loops of opioid receptors while opioids bind to extracellular loops of adrenergic receptors. Thus, each compound type can bind to the complementary receptor, enhancing the activity of the other compound type through an allosteric mechanism. Screening for ligand complementarity may permit the identification of other mutually-enhancing sets of compounds as well as the design of novel combination drugs or tethered compounds with improved duration and specificity of action.

Ocular Purine Receptors as Drug Targets in the Eye

Agonists and antagonists of various subtypes of G protein coupled adenosine receptors (ARs), P2Y receptors (P2YRs), and ATP-gated P2X receptor ion channels (P2XRs) are under consideration as agents for the treatment of ocular diseases, including glaucoma and dry eye. Numerous nucleoside and nonnucleoside modulators of the receptors are available as research tools and potential therapeutic molecules. Three of the 4 subtypes of ARs have been exploited with clinical candidate molecules for treatment of the eye: A1, A2A, and A3. An A1AR agonist is in clinical trials for glaucoma, A2AAR reduces neuroinflammation, A3AR protects retinal ganglion cells from apoptosis, and both A3AR agonists and antagonists had been reported to lower intraocular pressure (IOP). Extracellular concentrations of endogenous nucleotides, including dinucleoside polyphosphates, are increased in pathological states, activating P2Y and P2XRs throughout the eye. P2YR agonists, including P2Y2 and P2Y6, lower IOP. Antagonists of the P2X7R prevent the ATP-induced neuronal apoptosis in the retina. Thus, modulators of the purinome in the eye might be a source of new therapies for ocular diseases.

QM/MM methodology, docking and spectroscopic (FT-IR/FT-Raman, NMR, UV) and Fukui function analysis on adrenergic agonist

The Fourier transform infrared, FT-Raman, UV and NMR spectra of Ternelin have been recorded and analyzed. Harmonic vibrational frequencies have been investigated with the help of HF with 6-31G (d,p) and B3LYP with 6-31G (d,p) and LANL2DZ basis sets. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by GIAO method. The polarizability (α) and the first hyperpolarizability (β) values of the investigated molecule have been computed using DFT quantum mechanical calculations. Stability of the molecule arising from hyper conjugative interactions, and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The electron density-based local reactivity descriptors such as Fukui functions were calculated to explain the chemical selectivity or reactivity site in Ternelin. Finally the calculated results were compared to simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra. Molecular docking studies have been carried out in the active site of Ternelin and reactivity with ONIOM was also investigated.

GOMoDo: A GPCRs online modeling and docking webserver

G-protein coupled receptors (GPCRs) are a superfamily of cell signaling membrane proteins that include >750 members in the human genome alone. They are the largest family of drug targets. The vast diversity and relevance of GPCRs contrasts with the paucity of structures available: only 21 unique GPCR structures have been experimentally determined as of the beginning of 2013. User-friendly modeling and small molecule docking tools are thus in great demand. While both GPCR structural predictions and docking servers exist separately, with GOMoDo (GPCR Online Modeling and Docking), we provide a web server to seamlessly model GPCR structures and dock ligands to the models in a single consistent pipeline. GOMoDo can automatically perform template choice, homology modeling and either blind or information-driven docking by combining together proven, state of the art bioinformatic tools. The web server gives the user the possibility of guiding the whole procedure. The GOMoDo server is freely accessible at http://molsim.sci.univr.it/gomodo.

Development and validation of a sensitive LC-MS/MS method for the determination of fenoterol in human plasma and urine samples

Due to the lack of sensitivity in current methods for the determination of fenoterol (Fen), a rapid LC-MS/MS method was developed for the determination of (R,R')-Fen and (R,R';S,S')-Fen in plasma and urine. The method was fully validated and was linear from 50pg/ml to 2000pg/ml for plasma and from 2.500ng/ml to 160ng/ml for urine with a lower limit of quantitation of 52.8pg/ml in plasma. The coefficient of variation was <15% for the high QC standards and <10% for the low QC standards in plasma and was <15% for the high and low QC standards in urine. The relative concentrations of (R,R')-Fen and (S,S')-Fen were determined using a chirobiotic T chiral stationary phase. The method was used to determine the concentration of (R,R')-Fen in plasma and urine samples obtained in an oral cross-over study of (R,R')-Fen and (R,R';S,S')-Fen formulations. The results demonstrated a potential pre-systemic enantioselective interaction in which the (S,S')-Fen reduces the sulfation of the active (R,R')-Fen. The data suggest that a non-racemic mixture of the Fen enantiomers may provide better bioavailability of the active (R,R')-Fen for use in the treatment of cardiovascular disease.

Effects of synephrine and beta-phenethylamine on human alpha-adrenoceptor subtypes

Synephrine and beta-phenethylamine, two naturally occurring compounds, are structurally related to ephedrine. In this study, the effects of synephrine and beta-phenethylamine on alpha-adrenergic receptor (alpha-AR) subtypes are investigated in human embryonic kidney (HEK293) or Chinese hamster ovary (CHO) cells, and compared to that of 1R,2S-norephedrine. The rank order of binding affinities was found to be the same for the subtypes tested (alpha(1A)-, alpha(2A)-, and alpha(2C)-AR) viz, 1R,2S-norephedrine > beta-phenethylamine > synephrine. Functional studies on the alpha(1A)-AR subtype showed that synephrine was a partial agonist giving a maximal response at 100 microM that was equal to 55.3 % of the L-phenylephrine maximum. In contrast, neither 1R,2S-norephedrine nor beta-phenethylamine exhibited agonist activity at the highest concentration tested (300 microM). beta-Phenethylamine was more potent as an antagonist than 1R,2S-norephedrine and synephrine on the alpha(1A)-AR subtype. Functional studies on the alpha(2A)- and alpha(2C)-AR subtypes indicated that synephrine and beta-phenethylamine did not act as agonists. Similar to 1R,2S-norephedrine, both of these analogs reversed the effect of medetomidine against forskolin-induced cAMP elevations at 300 microM, and the rank order of antagonist potency was: 1R,2S-norephedrine = beta-phenethylamine > synephrine; and beta-phenethylamine > 1R,2S-norephedrine > synephrine, respectively. These differences suggest that the presence of a 4-hydroxy group, as in synephrine, reduced the potency in these subtypes. In conclusion, at the alpha(1A)-AR, synephrine acted as a partial agonist, while beta-phenethylamine did not exhibit any direct agonist activity. Both, synephrine and beta-phenethylamine, may act as antagonists of pre-synaptic alpha(2A/2C)-ARs present in nerve terminals.

Total synthesis and biological evaluation of the marine bromopyrrole alkaloid dispyrin: elucidation of discrete molecular targets with therapeutic potential

The first total synthesis of dispyrin, a recently reported bromopyrrole alkaloid from Agelas dispar with an unprecedented bromopyrrole tyramine motif, was achieved in three steps on a gram scale (68.4% overall). No biological activity was reported for dispyrin, so we evaluated synthetic dispyrin against>200 discrete molecular targets in radioligand binding and functional assays. Unlike most marine natural products, dispyrin (1) possesses no antibacterial or anticancer activity, but was found to be a potent ligand and antagonist of several therapeutically relevant GPCRs, the alpha1D and alpha2A adrenergic receptors and the H2 and H3 histamine receptors.

Retention prediction of adrenoreceptor agonists and antagonists on a diol column in hydrophilic interaction chromatography

Retention prediction models using multiple linear regression (MLR) and artificial neural networks (ANN) were developed for adrenoreceptor agonists and antagonists chromatographed on a diol column under hydrophilic interaction chromatographic (HILIC) mode at three pH conditions (3.0, 4.0 and 5.0). Using stepwise MLR, the retention behavior of the analytes was satisfactorily described by a five-predictor model; the predictors being the percentage of acetonitrile in the mobile phase (% ACN), the logarithm of partition coefficient (log D), the number of hydrogen bond donor (HBD), the number of hydrogen bond acceptor (HBA), and the total absolute atomic charge of the molecule (TAAC). Among the five descriptors, % ACN had the strongest effect on the retention as indicated by its relatively higher standardized coefficient compared to the other four predictors. The inclusion of the four predictors which are related to the properties of the compounds (log D, HBD, HBA and TAAC), suggested hydrophilic interaction, hydrogen bonding and ionic interaction as possible mechanisms of retention of the analytes on the studied system. The models derived from MLR also showed adequate fit as proven by the high correlation (R2 as high as 0.9667) between observed and predicted log k values for the training set and good predictive power on the test set (R2 greater than 0.97). ANN analyses of the data were also conducted using the five predictors derived from MLR as inputs and log k as output. The trained ANNs showed better predictive abilities as compared to MLR models as indicated by relative higher R2 and lower root mean square error of predictions (RMSEP) for both training and test sets. The derived models can be used as references for method development and optimization of chromatographic conditions for the separation of adrenoreceptor agonists and antagonists.

Retention prediction of adrenoreceptor agonists and antagonists on unmodified silica phase in hydrophilic interaction chromatography

The development of retention prediction models for adrenoreceptor agonists and antagonists chromatographed on an unmodified silica stationary phase under the hydrophilic interaction chromatographic (HILIC) mode at three pH conditions (3.0, 4.0 and 5.0) is described. The models were derived using multiple linear regression (MLR) and an artificial neural network (ANN) using the logarithm of the retention factor (log k) as the dependent variable. In addition to the effects of the solute-related variables (molecular descriptors), the percentage of acetonitrile (%ACN) was also used as a predictor to gauge the influence of the mobile phase on the retention behavior of the analytes. Using stepwise MLR, the retention behavior of the studied compounds at pH 3.0 were satisfactorily described by a four-predictor model; the predictors being the %ACN, the logarithm of the partition coefficient (log D), the number of hydrogen bond acceptors (HBA), and the magnitude of the dipole moment (DipolMag). In addition to these four predictors, the total absolute atomic charge (TAAC) was found to be a significant predictor of retention at pH 4.0 and 5.0. Among the five descriptors, %ACN had the strongest effect on the retention, as indicated by its higher standardized coefficient than those obtained for the other four predictors. The inclusion of these four predictors which are related to the molecular properties of the compounds (log D, HBA, DipolMag, and TAAC) suggested that hydrophilic interactions, hydrogen bonding and ionic interactions are possible mechanisms by which analytes are retained on the studied system. The reliability and predictive ability of the derived MLR equations were tested using cross-validation and a test set which was not used when fitting the model. The models derived from MLR produced adequate fits, as proven by the high R2 values obtained for all calibration and training sets (0.9497 and above), and their good predictive power, as indicated by the high cross-validated q2 (0.9465 and above) and high R2 (0.9305 and above) values obtained for the test sets. ANN prediction models were also derived using the predictors derived from MLR as inputs and log k as output. A comparison of the models derived from both ANN and MLR revealed that the trained ANNs showed better predictive abilities than the MLR models, as indicated by their higher R2 values and their lower root mean square error of predictions (RMSEP) for both training and test sets under all pH conditions. The derived models can be used as references and they provide a useful tool for method development and the optimization of chromatographic conditions for the separation of adrenoreceptor agonists and antagonists.

Mutagenesis within Helix 6 of the Human β1-Adrenergic Receptor Identifies Lysine324as a Residue Involved in Imparting the High-Affinity Binding State of Agonists

Competition binding isotherms for agonists to G protein-coupled receptors (GPCR) display high and low binding affinities. Mutagenesis of lysine at position 324 in helix 6 of the wild-type (WT) human beta1-adrenergic receptor (beta1-AR) generated mutant receptors that had GTP-insensitive single low-affinity binding sites for agonists and reduced potencies of full or partial agonists in stimulating adenylyl cyclase. Unlike the WT beta1-AR, intrinsic activities of full and partial agonists in activating the Lys324-->Ala beta1-AR (K324A) mutant were correlated with their binding affinities to the K324A mutant. In assays, such as agonist-mediated phosphorylation and recycling, the K324A mutant and the WT beta1-AR behaved similarly. However, in fluorescence resonance energy transfer assays that determined the proximity between the WT beta1-AR or the K324A mutant to G(s)alpha, there were significant differences. The conceptual framework of the ternary complex model could not adequately account for the behavior of the K324A mutant except under assumptions of low receptor-G protein binding affinities. The single low-affinity binding site of the K324A mutant to isoproterenol was converted by the C-terminal 11-amino-acid peptide of G(s)alpha, which acts a GDP-bound G(s)alpha mimic, to high- and low-affinity sites. Based upon the three-dimensional architecture of the human beta1-AR, the distance between Lys324 and the Asp/Glu-Arg-Tyr motif in helix 3 was the shortest among the various amino acids in helix 6. These findings indicate that Lys324 lies in a groove between helices 3 and 6, and its mutagenesis generates a mutant receptor with very low binding affinity for the GDP-bound isoform of G(s).

Molecular evolution of adrenoceptors and dopamine receptors: implications for the binding of catecholamines

We derived homology models for all human catecholamine-binding GPCRs (CABRs; the alpha-1, alpha-2, and beta-adrenoceptors and the D1-type and D2-type dopamine receptor) using the bovine rhodopsin-11-cis-retinal X-ray structure. Interactions were predicted from the endogenous ligands norepinephrine or dopamine and from the binding site and were used to optimize receptor-ligand interactions. Similar binding modes in the complexes agree with a large "binding core" conserved across the CABRs, that is, D3.32, V(I)3.33, T3.37, S5.42, S(A/C)5.43, S5.46, F6.51, F6.52, and W6.48. Model structures and docking simulations suggest that extracellular loop 2 could provide a common attachment point for the ligands' beta-hydroxyl via a hydrogen bond donated by the main-chain NH group of residue xl2.52. The modeled CABRs and docking modes are in good agreement with published experimental studies. Complementarity between the ligand and the binding site suggests that the bovine rhodopsin structure is a suitable template for modeling agonist-bound CABRs.

Recent developments in the design of orally bioavailable beta3-adrenergic receptor agonists

The beta3-adrenergic receptor (beta3-AR) has been shown to mediate various pharmacological and physiological effects such as lipolysis, thermogenesis, and relaxation of the urinary bladder. Activation of the beta3-AR is thought to be a possible approach for the treatment of obesity, type 2 diabetes mellitus, and frequent urination. Therefore, the beta3-AR is recognized as an attractive target for drug discovery. On the other hand, activation of the beta1- or beta2-AR can cause undesirable side effects such as increased heart rate or muscle tremors. Consequently, a number of recent efforts in this field have been directed toward the design of selective agonists for the beta3-AR. This review summarizes recent advances in beta3-AR agonists with an emphasis on recent attempts to create potent, selective and orally bioavailable small-molecule agonists.

The Thermodynamics of the Partitioning of Ionizing Molecules Between Aqueous Buffers and Phospholipid Membranes

PURPOSE

To study the thermodynamics of partitioning of eight ionising dual D2-recepto beta2-adrenoceptor agonists between vesicles of L-alpha-dimyristoylphosphatidylcholine (DMPC) and aqueous buffers.

METHODS

The thermodynamics of partitioning have been studied by isothermal titration calorimetry (ITC).

RESULTS

Compounds which are predominantly cationic at pH 7.4 (designated as class 1 compounds) have a more exothermic partitioning than those which are predominantly in the electronically neutral form (designated as class 2 compounds) at pH 7.4, and less positive standard entropies of partitioning. Under acidic conditions (pH 4.0), class compounds 2 (predominantly electronically neutral at pH 7.4) are almost completely cationic and accordingly have a more exothermic partitioning than at pH 7.4. The standard entropies of partitioning also depend on the pH. When the compounds are predominantly cationic, the standard entropy change is less positive (less favourable) than under conditions where the compounds are predominantly electronically neutral.

CONCLUSIONS

The observations are consistent with the notion of there being a favourable electrostatic interaction (enthalpically) between the positively charged amino-group of predominantly cationic compounds and the negatively charged phosphate group of the vesicle.

G-protein coupled receptors: SAR analyses of neurotransmitters and antagonists

BACKGROUND

From the deductive point of view, neurotransmitter receptors can be divided into categories such as cholinergic (muscarinic, nicotinic), adrenergic (alpha- and beta-), dopaminergic, serotoninergic (5-HT1 approximately 5-HT5), and histaminergic (H1 and H2). Selective agonists and antagonists of each receptor subtype can have specific useful therapeutic applications. For understanding the molecular mechanisms of action, an inductive method of analysis is useful.

OBJECTIVE

The aim of the present study is to examine the structure-activity relationships of agents acting on G-protein coupled receptors.

METHOD

Representative sets of G-PCR agonists and antagonists were identified from the literature and Medline [P.M. Walsh (2003) Physicians' Desk Reference; M.J. O'Neil (2001) The Merck Index]. The molecular weight (MW), calculated logarithm of octanol/water partition coefficient (C log P) and molar refraction (CMR), dipole moment (DM), E(lumo) (the energy of the lowest unoccupied molecular orbital, a measure of the electron affinity of a molecule and its reactivity as an electrophile), E(homo) (the energy of the highest occupied molecular orbital, related to the ionization potential of a molecule, and its reactivity as a nucleophile), and the total number of hydrogen bonds (H(b)) (donors and receptors), were chosen as molecular descriptors for SAR analyses.

RESULTS

The data suggest that not only do neurotransmitters share common structural features but their receptors belong to the same ensemble of G-protein coupled receptor with seven to eight transmembrane domains with their resultant dipoles in an antiparallel configuration. Moreover, the analysis indicates that the receptor exists in a dynamic equilibrium between the closed state and the open state. The energy needed to open the closed state is provided by the hydrolysis of GTP. A composite 3-D parameter frame setting of all the neurotransmitter agonists and antagonists are presented using MW, Hb and mu as independent variables.

CONCLUSION

It appears that all neurotransmitters examined in this study operate by a similar mechanism with the G-protein coupled receptors.

Plasmon-waveguide resonance studies of ligand binding to the human beta 2-adrenergic receptor

Plasmon-waveguide resonance (PWR) spectroscopy is an optical technique that can be used to probe the molecular interactions occurring within anisotropic proteolipid membranes in real time without requiring molecular labeling. This method directly monitors mass density, conformation, and molecular orientation changes occurring in such systems and allows determination of protein-ligand binding constants and binding kinetics. In the present study, PWR has been used to monitor the incorporation of the human beta(2)-adrenergic receptor into a solid-supported egg phosphatidylcholine lipid bilayer and to follow the binding of full agonists (isoproterenol, epinephrine), a partial agonist (dobutamine), an antagonist (alprenolol), and an inverse agonist (ICI-118,551) to the receptor. The combination of differences in binding kinetics and the PWR spectral changes point to the occurrence of multiple conformations that are characteristic of the type of ligand, reflecting differences in the receptor structural states produced by the binding process. These results provide new evidence for the conformational heterogeneity of the liganded states formed by the beta(2)-adrenergic receptor.

Application of the Lewis acid-Lewis base bifunctional asymmetric catalysts to pharmaceutical syntheses: stereoselective chiral building block syntheses of human immunodeficiency virus (HIV) protease inhibitor and beta3-adenergic receptor agonist

Chiral building block syntheses of promising drugs were achieved using two types of catalytic stereoselective cyanosilylations of aldehydes promoted by Lewis acid-Lewis base bifunctional catalysts 1 and 2 as the key steps (diastereoselective cyanosilylation of amino aldehyde and enantioselective cyanosilylation). In the first part of this article, syntheses of chiral building blocks (6) of Atazanavir (3: human immunodeficiency virus (HIV) protease inhibitor) using the bifunctional catalyst 2 are discussed. The reaction of Boc-protected phenylalaninal 21 in the presence of 1 mol% catalyst 2 selectively afforded the anti isomer 22 as the major product (diastereomeric ratio=97 : 3), which was successively converted to the corresponding epoxide 6 in six steps. In the second part, we describe a chiral building block synthesis of beta(3)-adrenergic receptor agonists. The enantioselective cyanosilylation of 3-chlorobenzaldehyde (38) with 9 mol% catalyst 1 gave the chiral cyanohydrin 39, which was converted to beta-hydroxyethylamine 40 by reduction. Moreover, the chiral ligand of catalyst 1 could be recovered without column chromatography and reused without decreasing its activity.

Conformationally restrained analogues of sympathomimetic catecholamines. Synthesis and adrenergic activity of 5,6- and 6,7-dihydroxy-3,4-dihydrospiro[naphthalen-1(2H)-2',5'-morpholines]

The 5,6- (10a) and 6,7-dihydroxy-3,4-dihydrospiro[naphthalen-1(2H)-)-2',5'-morpholine](11a) and their N-isopropyl derivatives (10b and 11b) (DDSNMs), which can be viewed as the result of the combination of the structure of the 2-(3,4-dihydroxyphenyl)morpholine 5a or 5b (DPMs) with the structure of the corresponding 1-(aminomethyl)-5,6-dihydroxy- (8a or 8b) or 1-(aminomethyl)-6,7-dihydroxy-1,2,3,4-tetrahydro-1-naphthalen-ol (9a or 9b) (1-AMDTNs) were synthesised. The new compounds DDSNMs 10a,b and 11a,b were assayed for their alpha- and beta-adrenergic properties by means of binding experiments and functional tests and the results were compared with those obtained for catecholamines 1a, b and the previously described morpholine (5) and tetrahydronaphthalene (8, 9) derivatives. The affinity and activity indices thus obtained indicate in general a low ability of the new compounds 10 and 11 to interact with the alpha- and beta-adrenoceptors, which, in all cases, was lower than that of the corresponding morpholine (5) and tetrahydronaphthalene (8, 9) analogues.

BMS-196085: a potent and selective full agonist of the human beta(3) adrenergic receptor

A series of 4-hydroxy-3-methylsulfonanilido-1,2-diarylethylamines were prepared and evaluated for their human beta(3) adrenergic receptor agonist activity. SAR studies led to the identification of BMS-196085 (25), a potent beta(3) full agonist (K(i)=21 nM, 95% activation) with partial agonist (45%) activity at the beta(1) receptor. Based on its desirable in vitro and in vivo properties, BMS-196085 was chosen for clinical evaluation.

Separation of basic drug enantiomers by capillary zone electrophoresis using glucuronyl glucosyl beta-cyclodextrin as a chiral selector

Separations of basic drug enantiomers have been investigated using glucuronyl glucosyl beta-cyclodextrin (GUG beta-CD) as a chiral selector in the background electrolyte by capillary zone electrophoresis. The effects of GUG beta-CD concentration and running buffer pH on the migration times and resolution of 16 basic drug enantiomers were precisely examined using a linear polyacrylamide-coated capillary. High resolution of 16 basic drug enantiomers was generally attained with a running buffer pH 2.5 or 3.5 containing 10 mM GUG beta-CD. Next, we compared the chiral resolution abilities of GUG beta-CD with those of beta-CD and maltosyl beta-CD (G2 beta-CD). GUG beta-CD showed higher resolution for basic drug enantiomers tested than beta-CD and G2 beta-CD. This could be due to that hydrogen bonding or ionic interactions of uncharged and charged glucuronyl glucosyl groups of GUG beta-CD with an analyte could stabilize the inclusion complex.

Quantitative structure-activity relationship study of novel alpha1a-selective adrenoceptor antagonists

Two series of compounds were recently reported as novel alpha1a-selective adrenoceptor antagonists. In the first series, a dihydropyrimidone moiety is attached to a 4-phenyl piperidine containing side chain, while in the second, it is linked to a 4-substituted phenyl piperazine containing side chain. These compounds having potential for the treatment of benign prostatic hyperplasia, a urological disorder in the older age male population, were subjected to a quantitative structure-activity relationship study. The analysis has helped to ascertain the role of different substituents in explaining the observed binding potencies of these analogues. In the first category of compounds, three sites R1, R2, and X were varied and from the quantitative structure-activity relationship, it emerged that X- and R1-substituents having respectively, the high values of field and resonance effects may lead to more potent alpha1a-antagonists. The substituent of R2, being either CH3 or C2H5, does not add to improve the activity and thus the site, at present, becomes redundant. This site may, however, be explored for some additional substituents in future. In the second series of compounds, the phenyl ring, linked to a piperazine moiety at the end of a side chain, was substituted with various groups onto different positions. From derived significant correlations, it appeared the less polar and/or bulky substituents at the meta- and para-positions and a more hydrophobic substituent at the para-position are advantageous.

Synthesis and adrenergic activity of a new series of N-aryl dicyclopropyl ketone oxime ethers: SAR and stereochemical aspects

A novel series of 31 N-aryl dicyclopropyl ketone oxime ethers were synthesized and tested for their activity at alpha- and beta-adrenergic receptors. All of the compounds showed greater affinity for beta-than for alpha1-receptor sites. Some compounds had pure antagonist effects whereas some were partial agonists. Several compounds had an antagonist effect matching that of propranolol in in vitro (binding data and pA2 values on rat heart ventricle homogenates and guinea pig spontaneously beating right and electrically driven left atrial isolated preparations, respectively) and in in vivo tests (measurement of antagonism toward isoprenaline-induced tachycardia in anesthetized rats). Furthermore, all of the compounds showed a beta1-adrenergic selectivity (beta2-affinity > 1500 nM).

A molecular dynamics approach to receptor mapping: application to the 5HT3 and beta 2-adrenergic receptors

A molecular dynamics-based approach to receptor mapping is proposed, based on the method of Rizzi (Rizzi, J. P.; et al. J. Med. Chem. 1990, 33, 2721). In Rizzi's method, the interaction energy between a series of drug molecules and probe atoms (which mimic functional groups on the receptor, such as hydrogen bond donors) was calculated. These interactions were calculated on a three-dimensional grid within a molecular mechanics parameters, were placed at these minima. The distances between the dummy atom sites were monitored during molecular dynamics simulations and plotted as distance distribution functions. Important distances within the receptor became apparent, as drugs with a common mode of binding share similar peaks in the distance distribution functions. In the case of specific 5HT3 ligands, the important donor--acceptor distance within the receptor has a range of ca. 7.9--8.9 A. In the case of specific beta 2-adrenergic ligands, the important donor--acceptor distances within the receptor lie between ca. 7--9 A and between 8 and 10 A. These distances distribution functions were used to assess three different models of the beta 2-adrenergic G-protein-coupled receptor. The comparison of the distance distribution functions for the simulation with the actual donor--acceptor distances in the receptor models suggested that two of the three receptor models were much more consistent with the receptor-mapping studies. These receptor-mapping studies gave support for the use of rhodopsin, rather than the bacteriorhodopsin template, for modeling G-protein-coupled receptors but also sounded a warning that agreement with binding data from site-directed mutagenesis experiments does not necessarily validate a receptor model.

Photolabile "caged" adrenergic receptor agonists and related model compounds

The synthesis and photochemical characterization of caged derivatives of the adrenergic receptor agonists phenylephrine, epinephrine and isoproterenol are described. These compounds were prepared using 2-nitrobenzyl or substituted 2-nitrobenzyl photolabile protecting groups, and were designed to allow agonist concentration jumps to be made during pharmacological/physiological experiments. The advantage of this approach over conventional methods for changing the concentrations of agonists near receptors in mechanistic studies is the exquisite spatial and temporal resolution afforded by the use of light. Flash photolysis experiments revealed that photorelease is more than two orders of magnitude faster when the 2-nitrobenzyl group is attached to the beta-amino group rather than one of the phenolic oxygens of the catecholamine. For the caged phenylephrine derivatives, for example, the rate constants of release from the N-linked and O-linked derivatives are 1.8 x 10(4) s-1 and 1.1 x 10(2) s-1 respectively. However, the quantum yields of photorelease from the N-linked and O-linked derivatives are similar. In addition, several model compounds were prepared to allow examination of the effects of substituents on the aromatic ring and benzylic carbon (of the 2-nitrobenzyl moiety) on the rates and efficiencies of photorelease. These studies revealed that, although substituents had little effect on the rates of photorelease from the N-linked caged derivatives, electron-donating groups on the 2-nitrobenzyl ring increased the quantum yield of release by approximately fourfold, from 0.10 to 0.40. A summary of the studies completed to evaluate the biological properties of the caged adrenergic receptor agonists is also presented.

Evaluation of the role of GTP hydrolysis in the interaction between Mg2+ and GTP in regulating agonist binding to the adenosine A1 receptor

Binding of agonists to adenosine receptors is reduced by GTP, whereas it is enhanced by Mg2+. The effect of GTP can be completely reversed by divalent cations, in contrast to the effect of the nonhydrolyzable analogue 5'-guanylylimidodiphosphate (GPPNHP). The present study addresses the role of divalent cation-stimulated specific and nonspecific GTP-ases in this reversal process. Under the conditions commonly employed in binding assays, almost all GTP is rapidly converted to GMP and Pi, indicating that maintenance of GTP levels is essential for the proper interpretation of results. A combination of a GTP-generating system and a competing substrate for high Km GTP-ases minimizes GTP breakdown. In the presence of these additions, the reversal of GTP effects is almost eliminated, and the inhibitory effects of both GTP and GPPNHP on agonist binding are reduced by divalent cations to a similar extent. Besides enhancing nonspecific GTP hydrolysis, Mg2+, but not Mn2+ or Ca2+, also stimulates specific agonist-dependent GTP-ase activity. Thus, it is evident that specific regulatory effects of Mg2+ and other divalent cations can only be identified when other, nonspecific, effects have been evaluated and controlled.